1. Field of the Invention
This invention relates generally to the field of blow molded plastic containers, and more particularly to containers that are suitable for use with food or beverage products that are packaged using the hot fill process.
2. Description of the Related Technology
Many products that were previously packaged using glass containers are now being supplied in plastic containers, such as containers that are fabricated from polyesters such as polyethylene terephthalate (PET).
PET containers are lightweight, inexpensive, recyclable and can be economically manufactured in large quantities. PET therefore possesses excellent characteristics for containers, but PET resin is relatively expensive. Accordingly, a PET container design that reduces the amount of material that is used without sacrificing performance will provide a significant competitive advantage within the packaging industry.
PET containers are typically manufactured using the stretch blow molding process. This involves the use of a preform that is injection molded into a shape that facilitates distribution of the plastic material within the preform into the desired final shape of the container. The preform is first heated and then is longitudinally stretched and subsequently inflated within a mold cavity so that it assumes the desired final shape of the container. As the preform is inflated, it takes on the shape of the mold cavity. The polymer solidifies upon contacting the cooler surface of the mold, and the finished hollow container is subsequently ejected from the mold.
PET containers are particularly common for use in packaging beverages such as juices using what is known in the industry as the hot-fill process. This involves filling the containers while the liquid product is at an elevated temperature, typically 68° C.-96° C. (155° F.-205° F.) and usually about 85° C. (185° F.) in order to sterilize the container at the time of filling. Containers that are designed to withstand the process are known as “hot fill” or “heat set” containers.
Hot fill containers must be designed to be strong enough in the areas outside of the vacuum panel regions so that the deformation that occurs as a result of the volumetric shrinkage of a product within the container is substantially limited to the portions of the container that are designed specifically to accommodate such shrinkage. In addition, since filled containers are often stacked on top of one another for transportation and distribution, the sidewall of such containers must be designed to have sufficient column strength in order to endure a predetermined minimum vertical load. It is important that such column strength not be degraded as the shape of the container changes as result of volumetric shrinkage within the container.
Moreover, a hot fill container must possess adequate hoop or circumferential strength in order to avoid excessive outward and inward bowing during changes of temperature and pressure, as well as to provide sufficient crush resistance when the container is gripped by a consumer.
There is significant price competition within the plastic packaging industry, and the cost of plastic resin is one of the main components of the price of hot fill containers. There is a fundamental tension between the strength requirements of such containers and the economic necessity to use as little plastic resin as possible in order to provide a functional container. In order to optimize column strength and hoop strength, a variety of different designs have been commercialized, using various features such as ribs and grooves that are defined within the sidewall of the container during the molding process.
One type of hot fill container that is disclosed in U.S. Pat. No. 7,604,140 to Pritchett et al. utilizes a plurality of vacuum panels that are arranged in a twisted or helical fashion about the periphery of the container. Such a helical vacuum panel configuration possesses certain advantages, because it provides inherent reinforcement in both the longitudinally and circumferential directions. In addition, such containers can be aesthetically pleasing to many consumers. However, such containers would be usable for more commercial packaging applications if they had improved crush resistance.
A need exists for an improved hot fill type container employing twisted or helical vacuum panels that exhibits superior crush resistance with respect to conventional containers of this type without requiring significant additional material.